Promotion of Thermal Inactivation Treatment of Apple Polyphenol Oxidase in the Presence of Trehalose.

Abstract

Trehalose is known to protect enzymes from denaturation. In the present study, we observed promotion of apple polyphenol oxidase (PPO) inactivation in a trehalose solution with thermal treatment. Crude PPO from Fuji apple was mixed with either sucrose or trehalose solutions, then the samples treated at 25 or 65 °C. In the presence of trehalose, PPO activities were markedly decreased upon treatment at 65 °C with increasing trehalose concentration. Furthermore, the reduction in PPO activity in the presence of trehalose was proportional to storage time after thermal treatment and thermal treatment time. Comparing PPO activities between treatment time 0 and 90 min at 65 °C, activities decreased 89 % for trehalose concentration of 0.2 M. These results indicates that trehalose acts not only as inhibitor but as promoter of inactivation of PPO. The Lineweaver-Burk plot indicated that trehalose acts on PPO as a non-competitive inhibitor during the 65 °C treatment. Two mechanisms of PPO inactivation in the presence of trehalose were suggested; one is the suppression of PPO activation cause by a thermal treatment, and another is the conformational change to inactivation form of PPO in conjunction with trehalose and a thermal treatment. Additionally, apple juice including 0.2 or 0.5 M trehalose with 65 °C treatment indicated slow browning than the juice with 0.2 or 0.5 M sucrose or without sugars. This result demonstrates that the preventing of browning with trehalose is a viable industrial food process.